Generally used air-conditioning apparatuses having a multi-room heat-pump refrigeration cycle include an outdoor unit including a compressor, a four-way valve, and an outdoor heat exchanger, and a plurality of indoor units each including an expansion valve and an indoor heat exchanger (use side heat exchanger). These components sequentially communicate with one another through refrigerant pipes, and form a heat-pump refrigeration cycle. Specifically, the indoor units have a parallel configuration, and form a certain refrigeration cycle by switching between a cooling operation and a heating operation. Also, there are multi-room air-conditioning apparatuses capable of simultaneously performing a cooling operation and a heating operation.
Such multi-room air-conditioning apparatuses adjust a flow rate of the refrigerant in the entire refrigeration cycle by adjusting an operation capacity of the compressor using a condensing temperature of the indoor heat exchangers as a target value in the case of the heating operation. Also, each of the indoor units adjusts a flow rate of the refrigerant in the indoor heat exchanger by adjusting an opening degree of the expansion valve using a degree of subcooling of the indoor heat exchanger as a target value. That is, a capacity of the indoor heat exchanger is designed such that a certain heating performance is achieved for a load of the indoor unit by adjusting a condensing pressure and a degree of subcooling within predetermined ranges in the case of the heating operation. In the case of the cooling operation, an evaporating pressure and a degree of superheat are adjusted within predetermined ranges.
Also, in the case where a multi-room air-conditioning apparatus capable of performing a simultaneous cooling and heating operation performs the simultaneous cooling and heating operation, during a cooling main operation in which the load of the cooling operation is large in terms of a load ratio between the load of the cooling operation and the load of the heating operation of the indoor units, the outdoor heat exchanger functions as a condenser in general. An amount of heat transferred in the outdoor heat exchanger is adjusted using, as a target value, the condensing temperature of the indoor heat exchanger of the indoor unit that is performing the heating operation.
Also, there has been proposed an air-conditioning apparatus including a controller that detects an operation mode of each of a plurality of indoor units and a difference between a temperature set in the indoor unit and a corresponding room temperature, determines an operation state of the entire air-conditioning apparatus using such information, and controls a capacity of a compressor and an amount of heat exchanged in an outdoor heat exchanger (see, for example, Patent Literature 1). When the largest value (MAXΔTjH) among ΔTj each representing a difference between a temperature set in a corresponding heating indoor unit and a temperature of sucked air is larger than an upper limit value α of a control target range in a cooling main operation mode, this air-conditioning apparatus determines that there is a unit whose performance is insufficient among the heating indoor units, and outputs a value obtained by subtracting Δffan from a current command value ffan of the rotation speed of an outdoor fan as a new command value ffan* to the outdoor fan. That is, when ΔTj of the indoor unit having the largest load among the heating indoor units is larger than the upper limit value α, the rotation speed of the outdoor fan is decreased.
In addition, as for air-conditioning apparatuses including a plurality of indoor units installed in the same room, there has been proposed an air-conditioning apparatus that performs an air-conditioning performance saving operation in any of the indoor units in the case where a detected air-conditioning load of a refrigerant circuit is larger than a heating performance rating preset for the refrigerant circuit (see, for example, Patent Literature 2). This air-conditioning apparatus determines whether a capacity of a compressor has reached the maximum capacity during the heating operation. Upon determining that the capacity of the compressor has reached the maximum value, the air-conditioning apparatus determines whether the performance of the entire system is sufficient or not for a heating load on the basis of a value obtained by subtracting a calculated high-pressure saturation temperature from a high-pressure saturation temperature target value. If the performance of the entire system seems to be insufficient, the air-conditioning apparatus changes a set degree-of-subcooling target value to a larger value in the order of ascending priority to perform a heating performance saving operation. In the case of the cooling operation, a set degree-of-superheat target value is changed to a larger value.